Design and testing of a Multi-Fuel industrial burner suitable for syn-gases, flare gas and pure hydrogen

Abstract

The complete design and validation procedure of a novel Multi-Fuel heavy-duty burner is illustrated, starting from the conception and CFD analysis, up to an extensive experimental campaign assessing the actual performance of an industrial scale prototype.The need for an innovative burner to be employed in utility boilers comes from the context of energy transition with still increasing steam demand for process/industrial applications. The capability to burn a wide range of fuels, going from natural gas to flare-gases, syn-gases and fuels with even lower heating values, up to pure hydrogen, with high efficiency and low emissions is mandatory: it is shown and explained how all the above tasks are pursued starting from the early stage of conceptual design, leading to the development of a 2.5 MW prototype; then the burner operation is studied more in depth by CFD analysis, with particular attention to the implementation of MILD combustion regime: internal recirculation along with mixing, namely fuel dilution in flue gases leads to distributed volumetric reaction with oxygen, involving low peak temperatures with high conversion efficiency. Furthermore, numerical analysis helps to investigate the effectiveness of a central stabilizing flame, the coupling between furnace and burner in view of the tests, and also helps to evaluate different injection patterns for the fuel jets.As a final step, a 1.5 MW prototype is tested in a refractory lined furnace: the performance is assessed with natural gas, either pure or diluted with nitrogen to mimic a low heating value syn-gas, and with increasing percentage of hydrogen up to 95% as thermal input. Different levels of input to the central stabilizing flame are tested, and excellent flame stability of burner operation is proven. NOx emissions decrease for lower heating value fuels, increase for hydrogen/natural gas mixtures up to 35% H2, and remain almost constant above this threshold. Though, keeping a very low excess of air and almost no carbon monoxide in the exit flue gases, the absolute NOx levels compare very well with state of the art Ultra-Low-NOx industrial burners developed for standard fossil fuels. The presented data set can be relevant both for industrial designers, as a reference for heavy-duty burners operating with a wide range of fuels, up to pure hydrogen, and for academic researchers investigating on combustion, even in MILD regime.